Method for forming openings in low dielectric constant material layer

ABSTRACT

The invention is directed towards a method for forming openings in low-k dielectric layers and a structure for forming an opening thereof. A mask layer comprising at least one metal hard mask layer and one or more hard mask layers is applied on the dielectric layer for forming the opening.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of prior applications Ser.No. 10/044,322, filed Jan. 10, 2002.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a method for manufacturingsemiconductor devices. More particularly, the present invention relatesto a method for forming openings in dielectric material layers.

2. Description of Related Art

In the semiconductor fabrication process, as the dimension of devices ona chip becomes smaller, the density of interconnect pitch becomeshigher. Because widely used silicon oxide dielectric layers have highdielectric constants, it can easily result in high RC delay. Therefore,low dielectric constant (low-k) dielectric material is used instead asan inter-metal dielectric (IMD) in high speed ICs. To apply low kdielectric has the advantage such as reducing the interconnectionparasitic capacitance, consequently reducing the RC delay, or mitigatingthe cross talk between metal lines, hence, the operation speed isimproved. Hence, the low k dielectric material is a very popular IMDmaterial used in high speed ICs.

The low k dielectric materials include inorganic materials, such as HSQ,FSG and CORAL, and organic materials, such as flare, SILK and parylene.

In the conventional via-first process for forming damascene opening, asshown in FIG. 1, a cap nitride layer 102 is formed over metalinterconnects (not shown) within a provided substrate 100. Afterwards, afirst low-k dielectric layer 104, a stop layer 106, a second low-kdielectric layer 108, a chemical mechanical polishing (CMP) stop layer110 and a bottom anti-reflection coating (BARC) layer (not shown) areformed in sequence on the cap nitride layer. Then, a patterned firstphotoresist layer is formed on the BARC layer for defining vias. Byusing the first photoresist layer as a mask and the cap nitride layer isused as an etching stop layer, a first anisotropic etching process isperformed through the layers to form a via opening.

After removing the first photoresist layer, a gap filling process isperformed to fill the via with a polymer material layer to protect thecap nitride layer. After a patterned second photoresist layer is formedon the polymer material layer, a second anisotropic etching process isperformed to define a trench, by using the stop layer as an etching stoplayer. FIG. 1 shows a prior-art damascene opening structure manufacturedby the cited above process.

However, the polymer material layer covering the via opening provokes afence profile 110 around top of the opening 120, as shown in FIG. 1. Itis because the polymer material layer hinders the etching, resulting inincomplete removal of the second low-k dielectric layer 108.

Furthermore, while the second photoresist layer is subsequently strippedby a photoresist removal process, such as a nitrogen/oxygen plasmaashing process or a nitrogen/hydrogen plasma process, the performedphotoresist removal process usually damages the side walls 107 of thesecond dielectric layer 108, leading to dielectric constant shift of thelow-k dielectric layer. Moreover, the low-k dielectric material of thedamaged sidewalls 107 tends to absorb moisture, resulting in degradationin the follow-up metallization process.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a method forforming openings in the dielectric material layer. The disadvantage ofphotoresist striping by plasma is improved, and no fence profile isprovoked. Therefore, it is more advantageous for the fabrication forforming openings in low-k material layers, especially the low-k materiallayers containing metal wires or interconnects.

To achieve these objects and advantages, and in accordance with thepurpose of the invention, as embodied and broadly described herein, theinvention is directed towards a method for forming openings in adielectric layer and a structure with an opening in the dielectriclayer. A dielectric layer is formed over the provided substrate, and thedielectric layer can be a single layer or comprises stack dielectriclayers of different dielectric materials. Preferably, the dielectriclayer is a low-k dielectric layer. A mask layer comprising at least ametal hard mask layer and a hard mask layer and a first anti-reflectionlayer are formed on the dielectric layer. A stop layer can be furtherincluded in the mask layer. The usage of the metal hard mask layer andthe hard mask layer is one of the advantageous features of the presentinvention. After patterning the mask layer, a second anti-reflectionlayer is formed. Using a patterned second photoresist layer formed onthe second anti-reflection layer as a mask, a via opening is defined.After removing the second photoresist layer along with the secondanti-reflection layer, a damascene opening is formed by using the masklayer as a mask.

The resultant structure with a damascene opening at least comprising:the substrate, the dielectric layer with the damascene opening and thepatterned mask layer that includes at least one metal hard mask layerand one or more hard mask layers on the dielectric layer. Before themask layer is patterned, the structure for forming the opening furtherincludes an anti-reflection layer on the mask layer.

By using the patterned mask layer comprising at least a metal hard masklayer as a mask along with the gap-filling anti-reflection layer, thedielectric layer is protected from plasma damage.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, and are intended toprovide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention. In the drawings,

FIG. 1 shows a prior art damascene opening structure manufactured by theconventional via-first process for forming damascene openings;

FIGS. 2A-2I are cross-sectional views of the process steps for forming adamascene opening in low-k material layers according to one preferredembodiment of this invention; and

FIGS. 3A-3H are cross-sectional views of the process steps for formingan opening in a dielectric layer according to another preferredembodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 2A-2I are cross-sectional views of the process steps for forming adamascene opening in low-k material layers according to one preferredembodiment of this invention.

Referring to FIG. 2A, a semiconductor substrate 200 having metal wires201 formed thereon is provided. A cap layer 202 is formed over thesubstrate 200 and the metal wires 201. The cap layer is, for example, anitride layer with a thickness of about 400-700 Å, preferably 500 Å.Afterwards, a first dielectric layer 204, an etch stop layer 206 and asecond dielectric layer 208 are formed in sequence on the cap nitridelayer 202. The first and second dielectric layers 202, 208 are low-kdielectric layers made of, for example, an inorganic polymer containingsilicon, such as CORAL™ or Black Diamond™. The first and seconddielectric layers 202, 208 are formed by, for example, CVD with athickness of about 2000 Å to 3000 Å. The thickness of the dielectriclayers is adjustable, depending on the structure formed on the substrate200. The etch stop layer 206 is, for example, a silicon nitride layer ora silicon carbide layer with a thickness of about 400-700 Å, preferably500 Å. Alternatively, the etch stop layer can be omitted.

Afterwards, a chemical mechanical polishing (CMP) stop layer 210, ametal hard mask layer 212, a hard mask layer 214 and a bottomanti-reflection coating (BARC) layer 216 are formed in sequence on thesecond dielectric layer 208. The CMP stop layer 210 is, for example, asilicon nitride layer or a silicon carbide layer with a thickness ofabout 400-700 Å, preferably 500 Å. Materials for forming the metal hardmask layer 212 includes tantalum, tantalum nitride, tungsten, tungstennitride, titanium nitride and titanium, formed by, for example, CVD orsputtering. The metal hard mask layer 212 has a thickness of about100-300 Å, preferably 200 Å. The hard mask layer 214 is, for example, asilicon nitride layer or a silicon carbide layer with a thickness ofabout 1000-2000 Å, preferably 1500 Å. The formation of the metal hardmask layer and the hard mask layer is one of the advantageous featuresof the present invention.

Afterwards, a patterned first photoresist layer 220 is formed on theBARC layer 216.

Referring to FIG. 2B, using the patterned photoresist layer 220 as amask, the BARC layer 216, the hard mask layer 214 and the metal hardmask layer 212 are partially removed until the CMP stop layer 210 isexposed. An opening 222 is thus formed within the BARC layer 216 a, thepatterned hard mask layer 214 a and the metal hard mask layer 212 a.

Referring to FIG. 2C, using plasma as a clean agent, the firstphotoresist layer 220 is removed. Because the material of the BARC layer216 is similar to the material of the photoresist layer 220, the BARClayer 216 a is removed along with the first photoresist layer 220.Because the dielectric layers 202, 208 are protected by the CMP stoplayer and not exposed to plasma, damage is thus avoided.

Referring to FIG. 2D, a BARC material layer 224 is formed by, forexample, spin-on, on the patterned hard mask layer 214a and fill theopening 222. The material for the BARC material layer 224 can be, forexample, fluid organic polymer, similar to the photoresist materials butwithout photosensitivity. The BARC material layer can act as ananti-reflection layer and fill the opening. Afterwards, a patternedsecond photoresist layer 230 is formed on the BARC material layer 224.

Referring to FIG. 2E, using the second photoresist layer 230 as a mask,a first anisotropic etching process is performed to remove the BARCmaterial layer 224, the CMP stop layer 210, the second dielectric layer208 and the etch stop layer 206, forming a via opening 232. The depth ofthe via opening 232 is adjustable, depending on the process needs. Thatis, the anisotropic etching can stop before, right at or after the etchstop layer 206, but without exposing the cap layer 202 and the metalwires.

Referring to FIG. 2F, a plasma process is performed to remove the secondphotoresist layer 230. Because the material of the BARC material layer224 is similar to the material of the photoresist layer 230, the BARCmaterial layer 224 is removed along with the second photoresist layer230.

Referring to FIG. 2G, using the hard mask layer 214 a and the metal hardmask layer 212 a as a mask, a second anisotropic etching process isperformed to form a damascene opening 234. The damascene opening 234includes a trench opening 234 a and a via opening 234 b. By controllingthe depth of the via opening 232 and the etching conditions, the trenchopening 234 a is etched until the etch stop layer 206 is exposed, whilethe via opening 234 b is formed by using the cap layer 202 as an etchstop layer.

Although sidewalls of the via opening 232 is exposed to plasma damagefor stripping the photoresist, the damaged sidewalls of the via opening232 is removed during the second anisotropic etching process.

Referring to FIG. 2H, the cap layer 202 is removed to expose theunderlying metal wires 201 within the substrate 200. The cap layer 202can be removed either by wet etching or dry etching. If the hard masklayer 214 a is made of the same material as the cap layer 202, forexample, silicon nitride, the hard mask layer 214 a is removed alongwith the cap layer 202.

Afterwards, a conductive layer (not shown) is formed to fill thedamascene opening 234. The material for forming the conductive layerincludes aluminum, copper or other metals formed by sputtering or CVD.The conductive layer is then planarized by CMP using the CMP stop layer210 as a polishing stop layer, so that a damascene interconnect 236 isformed within the opening 234, as shown in FIG. 2I. The metal hard masklayer 212 a and the CMP stop layer 210 are removed during the CMPprocess.

The following processes are well known to persons skilled in the art,and will not be further described therein.

By using the patterned hard mask layer and the patterned metal hard masklayer as a mask along with the gap-filling BARC material layer, thelow-k dielectric layers are protected from plasma damage for strippingthe photoresist. Moreover, no gap filling process is required for thevia opening, thus avoiding the fence profile.

FIGS. 3A-3H are cross-sectional views of the process steps for formingan opening in a dielectric layer according to another preferredembodiment of this invention.

Referring to FIG. 3A, a semiconductor substrate 300 is provided. If ametal wire 301 is included in the substrate 300, a cap layer 302 is thenformed on the substrate 300 and covering the metal wire 301. The caplayer is, for example, a nitride layer with a thickness of about 400-700Å, preferably 500 Å. Afterwards, a dielectric layer 304 is formed overthe substrate 300. The dielectric layer 304 can be a single layer orcomprises stack layers including a first dielectric layer and a seconddielectric layer. Optionally, a stop layer (not shown) can be includedbetween the first and the second dielectric layers. The dielectric layer304 is a low-k dielectric layer made of, for example, an inorganicpolymer containing silicon, such as CORAL™ or Black Diamond™. Thedielectric layer 304 is formed by, for example, CVD with a thickness ofabout 2000 Å to 3000 Å. For the dielectric layer 304 comprising stacklayers, the first and second dielectric layers can be made of differentdielectric materials, for example. The thickness of the dielectric layeris adjustable, depending on the structure formed on the substrate 300.Afterwards, a mask layer 306 is formed on the dielectric layer 304. Themask layer comprises at least a metal hard mask layer 310 and a hardmask layer 312. If needed, a chemical mechanical polishing (CMP) stoplayer 308 is further included in the mask layer 304. An anti-reflectioncoating (ARC) layer 314 is formed on the mask layer 306. The CMP stoplayer 308 is, for example, a silicon nitride layer or a silicon carbidelayer with a thickness of about 400-700 Å, preferably 500 Å. Materialsfor forming the metal hard mask layer 310 includes tantalum, tantalumnitride, tungsten, tungsten nitride, titanium nitride and titanium,formed by, for example, CVD or sputtering. The metal hard mask layer 310has a thickness of about 100-300 Å, preferably 200 Å. The hard masklayer 312 is, for example, a silicon nitride layer or a silicon carbidelayer with a thickness of about 1000-2000 Å, preferably 1500 Å. Theformation of the metal hard mask layer and the hard mask layer is one ofthe advantageous features of the present invention.

Afterwards, a patterned first photoresist layer 320 is formed on the ARClayer 314.

Referring to FIG. 3B, using the patterned photoresist layer 320 as amask, the ARC layer 314, the hard mask layer 312 and the metal hard masklayer 310 are partially removed until the CMP stop layer 308 is exposed.Therefore, the patterned mask layer 306 a (including the patterned hardmask layer 312 a and the metal hard mask layer 310 a) is obtained withan opening 322 formed within.

Referring to FIG. 3C, using plasma as a clean agent, the firstphotoresist layer 320 is removed. Because the material of the ARC layer314 is similar to the material of the photoresist layer 320, the ARClayer 314 a is removed along with the first photoresist layer 320.

Referring to FIG. 3D, an ARC material layer 324 is formed by, forexample, spin-on, on the patterned mask layer 306 a and fills theopening 322. The material for the ARC material layer 324 can be, forexample, fluid organic polymer, similar to the photoresist materials butwithout photosensitivity. The ARC material layer can act as ananti-reflection layer and fill the opening. Afterwards, a patternedsecond photoresist layer 330 is formed on the ARC material layer 324.

Referring to FIG. 3E, using the second photoresist layer 330 as a mask,a first anisotropic etching process is performed to partially remove theARC material layer 324, the CMP stop layer 308 and the dielectric layer304, forming a via opening 332. The depth of the via opening 332 isadjustable, depending on the process needs. That is, the anisotropicetching can stop in a first predetermined depth, but without exposingthe cap layer 202 and the metal wires.

Referring to FIG. 3F, a plasma process is performed to remove the secondphotoresist layer 330. Because the material of the ARC material layer324 is similar to the material of the photoresist layer 330, the ARCmaterial layer 324 is removed along with the second photoresist layer330.

Referring to FIG. 3G, using the patterned mask layer 306 a (i.e. thehard mask layer 312 a and the metal hard mask layer 310 a) as a mask, asecond anisotropic etching process is performed to form a damasceneopening 334. The damascene opening 334 includes a trench opening 334 aand a via opening 334 b. By controlling the depth of the via opening 332and the etching conditions, the trench opening 334 a is also etched to asecond predetermined depth, while the via opening 334 b is formed byusing the cap layer 302 as an etch stop layer.

The resultant structure with the damascene opening at least comprising:the substrate, the dielectric layer with the damascene opening and thepatterned mask layer that includes at least one metal hard mask layerand one or more hard mask layers on the dielectric layer. Before themask layer is patterned, the structure for forming the opening furtherincludes an anti-reflection layer on the mask layer.

Referring to FIG. 3H, the cap layer 302 is removed to expose theunderlying metal wires 301 within the substrate 300. The cap layer 302can be removed either by wet etching or dry etching. If the hard masklayer 312 is made of the same material as the cap layer 302, forexample, silicon nitride, the hard mask layer 312 a can be removed alongwith the cap layer 302. Afterwards, an interconnect (not shown) can beformed within the opening 334, as shown in FIG. 21. The followingprocesses are well known to persons skilled in the art, and will not befurther described therein.

However, the opening described herein is not limited to a damasceneopening. Other types of openings, including via openings, trenchopenings and contact openings are within the scope of the presentinvention.

By using the patterned mask layer as a mask along with the gap-fillingARC material layer, the dielectric layer is protected from plasmadamage.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncover modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

1-27. (canceled)
 28. A structure for forming an opening on a substrate,comprising: a first dielectric layer on the substrate; a seconddielectric layer on the dielectric layer; a plurality of mask layers atleast comprising a metal mask layer on the second dielectric layer; andan anti-reflection layer on the plurality of mask layers.
 29. Thestructure as claimed in claim 28, wherein materials for forming thefirst and second dielectric layers include inorganic polymer containingsilicon.
 30. The structure as claimed in claim 28, wherein theanti-reflection layer is a bottom anti-reflection coating layer made offluid organic polymer.
 31. The structure as claimed in claim 28, whereinthe metal mask layer is made of one of the following materials selectedfrom the group consisting of tantalum, tantalum nitride, titanium,titanium nitride, tungsten and tungsten nitride.
 32. The structure asclaimed in claim 28, wherein the mask layer is a silicon nitride layeror a silicon carbide layer.
 33. A structure for forming an opening on asubstrate, comprising: a first dielectric layer on the substrate; afirst stop layer on the first dielectric layer; a second dielectriclayer on the first stop layer; a third dielectric layer on the seconddielectric layer; a plurality of mask layers at least comprising a metalmask layer on the third dielectric layer; and an anti-reflection layeron the plurality of mask layers.
 34. The structure as claimed in claim33, wherein materials for forming the first and second dielectric layersinclude inorganic polymer containing silicon.
 35. The structure asclaimed in claim 33, wherein the anti-reflection layer is a bottomanti-reflection coating layer made of fluid organic polymer.
 36. Thestructure as claimed in claim 33, wherein the metal mask layer is madeof one of the following materials selected from the group consisting oftantalum, tantalum nitride, titanium, titanium nitride, tungsten andtungsten nitride.
 37. The structure as claimed in claim 33, wherein themask layer is a silicon nitride layer or a silicon carbide layer. 38.The structure as claimed in claim 33, wherein the first stop layer is asilicon nitride layer or a silicon carbide layer.
 39. The structure asclaimed in claim 33, wherein the third dielectric layer is a second stoplayer.
 40. A structure for forming an opening on a substrate,comprising: a dielectric layer on the substrate; a plurality of masklayers at least comprising a metal mask layer on the dielectric layer;and an anti-reflection layer on the plurality of mask layers.
 41. Thestructure as claimed in claim 40, wherein materials for forming thedielectric layer include inorganic polymer containing silicon.
 42. Thestructure as claimed in claim 40, wherein the anti-reflection layer is abottom anti-reflection coating layer made of fluid organic polymer. 43.The structure as claimed in claim 40, wherein the metal mask layer ismade of one of the following materials selected from the groupconsisting of tantalum, tantalum nitride, titanium, titanium nitride,tungsten and tungsten nitride.
 44. The structure as claimed in claim 40,wherein the mask layer is a silicon nitride layer or a silicon carbidelayer.
 45. A structure for forming an opening on a substrate,comprising: a first dielectric layer on the substrate; a stop layer onthe first dielectric layer; a second dielectric layer on the stop layer;a plurality of mask layers at least comprising a metal mask layer on thesecond dielectric layer; and an anti-reflection layer on the pluralityof mask layers.
 46. The structure as claimed in claim 45, whereinmaterials for forming the first and second dielectric layers includeinorganic polymer containing silicon.
 47. The structure as claimed inclaim 45, wherein the anti-reflection layer is a bottom anti-reflectioncoating layer made of fluid organic polymer.
 48. The structure asclaimed in claim 45, wherein the metal mask layer is made of one of thefollowing materials selected from the group consisting of tantalum,tantalum nitride, titanium, titanium nitride, tungsten and tungstennitride.
 49. The structure as claimed in claim 45, wherein the masklayer is a silicon nitride layer or a silicon carbide layer.
 50. Thestructure as claimed in claim 45, wherein the stop layer is a siliconnitride layer or a silicon carbide layer.